Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

On Feb 5, 2:40*pm, dumbstruck wrote:
Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

It could be that the valve is opening and closing rapidly causing
water hammer.

That answers your question. Now I suppose you are going to ask:

Why would a dishwasher fill valve open and close rapidly?

Could be:

1 - A faulty fill valve
2 - A faulty float switch sending erroneous signals to the control
board
3 - A faulty control board.

Cleaning the float switch would be my first suggestion.

Bench testing the valve would be my second (or test it in place with
an external power supply if possible)

I don't know how you would test the control board. Are there any
diagnostics listed in the manual?

On 2/5/2013 11:40, dumbstruck wrote:
Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

Have you checked your water pressure? Ideally it should be around 50
PSI. If it's considerably higher you need a reducing valve on the main
line.
--

On 2/5/2013 11:40, dumbstruck wrote:
Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

Have you checked your water pressure? Ideally it should be around 50
PSI. If it's considerably higher you need a reducing valve on the main
line.
--

On Tuesday, February 5, 2013 5:36:19 PM UTC-10, Bob wrote:
On 2/5/2013 11:40, dumbstruck wrote:

Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx



Have you checked your water pressure? Ideally it should be around 50

PSI. If it's considerably higher you need a reducing valve on the main

line.

--

Oh dear. It started when they raised our water pressure. From the scary sound, I took it as a sign to replace a severe kink in the feed pipe with a sharkbite, because i was warned here the kink would eventually leak. This went well for about a minute, then gave thunderous chattering.

Well, i have checked the float valve, and next will crank down the hot water valve down to near closed. I also may have pulled out a control wire when jamming the machine into its cubby hole. Yhanks all.

On Feb 5, 1:40*pm, dumbstruck wrote:
Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

Does it do it only once each time when the water shuts off because it
is sufficiently filled?

wrote in message
...

On Feb 5, 1:40 pm, dumbstruck wrote:
Why would a dishwasher make a hammering sound when filling? It severely
shakes the copper fill pipe. Thx

Does it do it only once each time when the water shuts off because it
is sufficiently filled?

***

Buy and install a water hammer arresting device as shown in this short video
clip. I have one on my dishwasher and washing machine and it solved the
problem.
http://youtu.be/vQf_qCYeeqs

On Wednesday, February 6, 2013 1:04:54 PM UTC-10, wrote:
On Feb 5, 1:40*pm, dumbstruck wrote:

Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx



Does it do it only once each time when the water shuts off because it

is sufficiently filled?

It make machine gun noises when filling, but not at other times. I did seem to hear the pipes filling at one point with no chattering. Our water pressure went up, but not to an unusual degree.

I would suspect that the problem is either a loose rubber washer in the water shut off valve used to isolate that dish washer, or that the cold water supply valve in the dish washer itself is worn out. Read on...

The fill valve on your toilet tank and the fill valves on dish washers and clothes washers all operated on the same principle. They all use the water pressure in the water supply piping to shut off the flow of water. That is done by having a rubber diaphragm covering the end of a pipe that supplies water to the toilet tank or appliance. The same full water pressure is applied to both sides of that rubber diaphragm, but one side of the diaphragm has a larger area exposed to that pressure than the other. The result is a "net" force holding the diaphragm down tightly over the end of the water supply pipe, thereby shutting the water flow off.

When you depress the toilet tank trip lever to flush the toilet, a mechanical linkage connected to the float pulls a plug out, thereby releasing the pressure on the large area side of the rubber diaphragm. That allows the rubber diaphragm to pop off the end of the water supply pipe and water flows into the toilet tank. (in a dish or clothes washer, this is done by an electromagnet that pulls a rubber tipped metal plug out of a hole in the rubber diaphram) Once the toilet tank fills back up again, the rising of the float pushes that plug back into place, and pressures once again equalize on both sides of the rubber diaphragm and the water flow shuts off.

Now, this kind of water shut off system is very fast acting. If water leaks around that plug so that the pressure on the large area side of the diaphragm is fluctuating, that can cause the rubber diaphragm to open and close very quickly, causing that hammering noise.

A similar thing can happen in a globe valve with a rubber washer when the screw holding the rubber washer in place is loose, and the rubber washer can move back and forth on that screw. If you think about it, in a typical shut off valve, the area of the rubber washer is larger than the area of the seat it covers. So, if there's water leakage between the screw and the washer hole, the area behind the rubber washer can become pressurized with water, causing the ruber washer to move forward, thereby shutting off the water flow. And, if the water behind the washer then leaks out, the pressure behind the washer drops so that the washer is pushed back again by the water supply pressure, opening the valve to water flow again. Because the volume behind the rubber washer is so small, that opening and closing of the valve can happen very quickly causing the rattling noise you heard and the shaking of the water supply piping.

So, I'd check the water shut off valve that isolates the dish washer for a loose washer screw first, and then replace the fill valve in the dish washer (or at least replace the rubber diaphragm in side it). I'd also check the electrical connection at that water fill valve to make sure a loose electrical connection isn't making that rubber tipped metal plug pop in and out of the hole in the rubber diaphragm, thereby causing the water fill valve to open and close in rapid succession (cuz that would cause the same symptoms).

On Wed, 6 Feb 2013 16:54:00 -0800 (PST), dumbstruck
wrote:

It make machine gun noises when filling, but not at other times.
I did seem to hear the pipes filling at one point with no chattering.
Our water pressure went up, but not to an unusual degree.

You already said this started when they raised your water pressure, so
you need to get a pressure regulator for the water source to that
dishwasher. go to a plumbing supply place and get one. Problem solved!

On Feb 6, 7:54*pm, dumbstruck wrote:
On Wednesday, February 6, 2013 1:04:54 PM UTC-10, wrote:
On Feb 5, 1:40*pm, dumbstruck wrote:

Why would a dishwasher make a hammering sound when filling? It severely shakes the copper fill pipe. Thx

Does it do it only once each time when the water shuts off because it

is sufficiently filled?

It make machine gun noises when filling, but not at other times. I did seem to hear the pipes filling at one point with no chattering. Our water pressure went up, but not to an unusual degree.

What would you consider a "usual degree"?

Have you checked the pressure before and after the pressure went up?
If the pressure was already approaching the upper limit of what the
fill valve was comfortable with, it wouldn't take much of an increase
to cause problems.

When my PRV valve failed, I didn't really notice much difference in
what came out of the faucets and showers, but the pipes would make a
bump-bump-bump sound for a few seconds after any fixture was turned
off. I put a pressure gauge on the utility sink and found that the
pressure was above the normal range of 55 - 60 and approaching 80. As
soon as I replaced the PRV, all the noise went away.

Head over to a hardware store and get one of these:

http://www.amazon.com/Rain-Bird-P2A-.../dp/B00004RACK

I don't know if you have a PRV in your system, but you want to make
sure that you test the pressure after the PRV, assuming the dishwasher
is after the PRV, which it should be. My house has a hose spigot in
the front and back that are at street pressure, so there's no sense in
me testing the pressure there. I have a utility sink with a "hose
connector faucet" that allows me check the pressure after the PRV.